I try not to under-estimate the intelligence of my readers, but couldn’t you be just a little more clueless? I mean, come on: virtually every person who left a comment realised that the ‘mystery animal’ from yesterday was a replica owl. Clearly, it was much, much easier than I thought. Anyway, well done everyone.
These owls are mostly based on Great horned owls Bubo virginianus, but the colour schemes are often a bit weird: the one I photographed has a red chest, though I doubt if this sort of thing makes much difference (hmm, or does it?). What’s amusing is that this particular decoy is at the top of Spinnaker Tower [shown below], a 170-metre-high visitor attraction located in the city of Portsmouth, UK. Spinnaker Tower was originally going to be called Millennium Tower, but construction didn’t start until 2001, and it wasn’t opened until 2005. It looks like the more famous Burj Al Arab in Dubai.
Anyway, I assumed that the owl was put there to scare off pigeons, but realised later that gulls (Herring gulls Larus argentatus) were more likely to be the target. Big owls – and I’m thinking in particular of the European eagle owl B. bubo – can be significant predators of gulls, so it follows that gulls would avoid them… but would this only be the case in gull populations where the gulls have suffered from owl predation?
One thing I’d really like to know about these decoys is how effective they are: birds are predominantly visual animals, and you might assume that they quickly become unafraid of decoys that are sat in the same spot for week, months or years. I’ve certainly seen pigeons sitting, unconcerned, just a few metres away from one of these decoys, and you can find a few observations in the literature which indicate that the decoys are indeed ineffective if left in the same place for any period of time. A study on the damage made by woodpeckers to utility poles found that decoy owls are only effective for a very limited time, and Andrews (1961), Conover (1985) and Montevecchi & Maccarone (1987) reported that thrushes, crows, and Grey jays Perisoreus canadensis, respectively, became habituated to owl decoys over time. Marsh et al. (1992) and Liebezeit & George (2002) concluded that immobile owl decoys are mostly ineffective against corvids. Incidentally, I’m greatly intrigued by the title of Conover’s paper: ‘Protecting vegetables from crows using an animated crow-killing owl model’. [UPDATE: thanks to Cameron McCormick I now know that Conover tested the effectiveness of a model that looks like it's killing a crow (see image below, from Conover (1985)). I was rather hoping that Conover was instead referring to a model owl equipped with motion-sensing lasers, heat-seeking missiles or tactical nukes, or perhaps to a robotic sentry gun disguised with feathers and a cute little owl face. Oh well]. Numerous anecdotes also indicate that the decoys are ineffective, and that pigeons, gulls, passerines and other birds will happily wander up to the decoys, sit on them, build nests on them, and so on…
Mobile owl decoys – they flap their wings – are commercially available, and are presumably far more effective. One problem exists, and it detracts from their use on tourist attractions like Spinnaker Tower: they look hilarious.
Refs – -
Andrews, R. J. 1961. The motivational behaviour controlling the mobbing calls of the blackbird (Turdus merula). III. Changes in the intensity of mobbing due to changes in the effect of the owl on the progressive waning of mobbing. Behaviour 18, 161-176.
Conover, M. R. 1985. Protecting vegetables from crows using an animated crow-killing owl model. Journal of Wildlife Management 49, 643-645.
Liebezeit, J. R. & George, T. L. 2002. A summary of predation by corvids on threatened and endangered species in California and management recommendations to reduce corvid predation. California Department of Fish and Game, Species Conservation and Recovery Program Report 2002-02, Sacramento, CA.
Marsh, R. E., Erickson, W. A. & Salmon, T. P. 1992. Scarecrows and predator models for frightening birds from specific areas. In Borrecco, J. E. & Marsh, R. E. (eds) Proceedings of the 15th vertebrate pest conference. University of California, Davis, pp. 112-114.
Montevecchi, W. A. & Maccarone, A. D. 1987. Differential effects of a Great horned owl decoy on the behaviour of juvenile and adult Gray jays. Journal of Field Ornithology 58, 148-151.